Biomass has been identified as a renewable energy source that can substitute some of the world's energy demands currently supplied by fossil fuels. Biomass is a particularly attractive alternative to coal and oil for heat and electricity generation and as a source of raw material for the production of fiber based products, conversion to liquid fuels, and as feedstock to gasification and pyrolysis processes.
Low quality has been the most significant technical challenge for the use of agricultural sourced biomass for these applications. High concentrations of inorganic minerals, also referred to as nutrients present in the biomass, including: nitrogen, phosphorous, potassium, chlorine, sodium, magnesium, calcium, silica and other inorganics, have significant negative impact on the quality of the biomass, especially if thermal conversion processes such as: combustion, gasification, and pyrolysis are used. These negative impacts include: (1) the formation of eutectic mixtures of silicates that significantly reduce the melting temperature of the biomass and resulting ash; (2) the formation of deposits, slags, and fouling in equipment at typical combustion temperatures; (3) corrosion and toxic air pollution; and (4) an overall reduction in thermal conversion efficiency in the power generation facility.
Forestry residues, such as wood chips and saw dust have lower concentrations of these inorganic nutrients, and as a result produce higher quality fiber. Biomass fiber from forestry have been used as feedstock for combustion gasification, pyrolysis, torrefaction and other industrial processes to produce: heat, electricity, ethanol, methanol, iso-butanol and other chemicals, and products such as: pulp, paper, fiberboard and clumping agent for cat litter. There are limits to how much biomass fiber can be sustainably harvested from the World's forests. Other sources of biomass such as crop residues, marginal and native grasses, and energy crops are an alternative source of biomass fiber if some of the quality issues can be addressed. One approach most commonly used to reduce inorganic nutrient content is field leaching. Field leaching refers to the natural leaching of plant material (including inorganic nutrients) left out in the field through a combination of rain, dew, mist and fog. Instead of harvesting the energy-crop or collecting residues at the time of harvest in early fall, the biomass is left in the field over the winter months and collected in early spring the following year. The various forms of precipitation over these months would naturally leach out a portion of the nutrients in the biomass.
While field leaching does remove some of the nutrients from the biomass, there are several disadvantages to the process that make field leaching inadequate for producing a consistent product that meets end-use quality requirements, including: (1) poor control of the process, with high susceptibility to weather variability; (2) contamination of the biomass from the soil; (3) partial reduction in inorganic nutrients resulting in high variability from farm to farm; (4) unpredictable and difficult scheduling of operations for subsequent crops; (5) only a viable option in moderate and colder climates since multiple growing seasons are possible in warmer climates and field leaching would severely interfere with the next crop rotation; (6) yield loss in organic matter of up to 40% in some crops; and (7) often net increase in ash content resulting from the non-leached nutrients predominately consisting of silica representing a higher percentage of the remaining material that has experienced 40% yield loss in organic matter.
An industrial process that could be used to extract inorganic minerals from a variety of biomass sources would be advantageous. It would be further advantageous if the inorganic minerals that are extracted could be refined by the process to produce a high-value co-product such as an inorganic fertilizer.
To date there are no technologies commercially available capable of extracting inorganic nutrients from biomass, and of co-producing a significantly improved biomass fiber and liquid inorganic fertilizer. Research conducted into the development of nutrient extraction processes for biomass has been limited and has failed to render a process that is either scalable for industrial use or economical. The disadvantages of approaches investigated by other researchers include: (1) very long biomass residence times requirements (24 hrs or more) limiting throughput; (2) very large volumes of water required (as high as 150:1 of water to biomass by weight); (3) requirements for bacteria, microbes, and chemicals to enable digestion, hydrolysis or acidification of biomass; (4) mostly batch processes that are difficult to scale-up; (5) very large reactor vessels and foot-print requirements (6) low nutrient extraction efficiency; (7) inadequate refinement of the extract renders the stream as a low-value by-product often needing disposal; and (8) need for fine comminution of the biomass, thus requiring more time and energy.
It would be desirable to develop a process that is capable of extracting substantially all of the inorganic nutrients from various sources of biomass. It would be further desirable if the process was able to remove: about 95% of the chlorine (Cl) in the biomass or more; about 90% of the potassium (K) in the biomass or more; about 80% of the phosphorous (P) in the biomass or more; about 70% of the magnesium (Mg) and sodium (Na) in the biomass or more; and at least about 40% of the nitrogen (N) in the biomass.
It would be further desirable if the process could achieve this in a continuous and compact reactor that requires less than 40 minutes biomass residence time in the reactor. A process that can achieve high extraction efficiency using only water as the extraction solvent at room-temperature reducing energy demands for the process, and at ratios as low as about 10:1 (water-to-biomass by weight). It would be further desirable if the process could allow for more than about 80% of the water used in the extraction process to be recycled within the process, thus reducing the demand for make-up water to the reactor. It would be further desirable if the about 20% of water exiting the process in the form of an extract could be refined to produce a product such as a liquid inorganic fertilizer.
The present invention presents an inventive process, which may serve to extract undesirable inorganic minerals (also referred to as inorganic nutrients) from various sources of plant-based biomass to produce inorganic fertilizer and/or co-produce a higher quality biomass fiber.
Further and other objects of the invention will be realized from the following Summary of the Invention, the Discussion of the Invention and the embodiments and Examples thereof.